This invention relates to an electrostatic process image forming machine, such as an electrostatic copier, printer or facsimile. More particularly, the invention relates to an image forming machine comprising image bearing means which may be a rotating drum or an endless belt, charging means for charging the image bearing means to a predetermined polarity, exposure means for selectively static-eliminating the charged image bearing means to form an electrostatic latent image, reversal development means for developing the electrostatic latent image on the image bearing means into a toner image, transfer means for transferring the toner image on the image bearing means onto an image receiving member which may be a plain paper, and cleaning means for removing a toner remaining on the image bearing means after transfer.
In the foregoing image forming machine, the charging means, which can be composed of a corona discharger, charges the image bearing means to a specific polarity over a predetermined effective charging width. The width of the image bearing means is larger than the effective charging width. On both sides of the effective charging width, the surface of the image bearing means is not stably charged to a predetermined potential, and can be of a potential considerably lower than the predetermined potential, or of substantially zero potential, or even of the opposite polarity. Development by the reversal development means does not apply a toner to a site where the charge potential remains, but applies the toner to a static elimination site where the charge potential has disappeared. In the image forming machine employing the reversal development means, therefore, the toner tends to adhere to both sides of the effective charging width on the surface of the image bearing means, thereby causing staining there. Even if an effective development width by the development means is rendered substantially the same as, or somewhat smaller than, the effective charging width, a floating toner, such as toner repelled by the charge potential on the image bearing means, can adhere onto the image bearing means on both sides of the effective charging width.
As transfer means in the image forming machine in the above-described configuration, a form composed of a transfer roller to receive a transfer voltage, or a form including an endless transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt has recently been proposed and put to practical use, instead of a transfer corona discharger. The transfer roller or transfer belt is brought into contact with the image bearing means via the image receiving member and directly over the entire width of the transfer roller or transfer belt. The transfer voltage applicator means is usually composed of a voltage applicator roller formed from an electrically conductive material and receiving a transfer voltage. The width of the voltage applicator roller is substantially the same as the width of the transfer belt, so that the transfer belt is contacted with the image bearing means over the entire width of the transfer belt, and given a transfer voltage over its entire width.
If the width of the transfer roller or transfer belt is larger than the aforementioned effective charging width, however, the transfer roller or transfer belt is brought into contact with the image bearing means not via the image receiving member, but directly on both sides of the effective charging width, because a maximum image receiving member is normally somewhat smaller than the effective charging width. As a result, the toner adhering to the image bearing means is transferred onto the transfer roller or transfer belt. Consequently, the surface of the transfer roller or transfer belt is stained with the toner. When both side portions of the face side of the transfer roller or transfer belt are stained with the toner, the state of contact between the image bearing means and the transfer roller or transfer belt is deteriorated, posing problems, such as poor transfer or damage to the surface of the image bearing means. To solve such problems, Japanese Patent No. 2597540 proposes that the width of the transfer roller (or transfer belt) be made smaller than the effective charging width.
If the width of the transfer roller or transfer belt is made smaller than the effective charging width, the toner adhering to the image bearing means on both sides of the effective charging width is prevented from being transferred to the transfer roller or transfer belt, but other problems occur. First, when the width of the transfer roller or transfer belt is made smaller than the effective charging width, the width of the transfer roller or transfer belt becomes nearly equal to or smaller than the width of the maximum image receiving member. As a result, the transportability of the image receiving member by the transfer roller or transfer belt lowers, causing a tendency toward a skew motion or a jam of the image receiving member. Secondly, particularly when the effective cleaning width of the cleaning means is substantially the same as or smaller than the effective charging width, the toner adhering to areas on both sides of the effective charging width on the surface of the image bearing means is not removed, but accumulated, thereby arousing the following phenomena: The accumulated toner accidentally floats, often contaminating the interior or surroundings of the image forming machine. Particularly, the floating toner adheres to the bearing mechanism of the transfer roller, or the bearing mechanism of a support roller for the transfer belt, the transfer voltage applicator means for the transfer roller or transfer belt, and so on, thereby not only staining these members, but also impeding their functions. Furthermore, the charging means, the reversal development means, and the cleaning means are provided with constituent elements extending or located widthwise outwardly of the effective charging width, the effective development width, and the effective cleaning width, respectively, for example, spacing setting rollers for setting spacing from the image bearing means sufficiently precisely, and various sealing members for preventing scatter of toner. The toner adhering to the areas on both sides of the effective charging width on the surface of the image bearing means stagnates and builds up between these constituent elements and the surface of the image bearing means. This is highly likely to destroy the spacing setting function of the spacing setting rollers, spoil the sealing function of the various sealing members, and damage the image bearing means, the spacing setting rollers, or the various sealing members.
The object of the present invention is to solve the above-described various problems, which are concerned with the toner adhering to both sides of the effective charging width on the surface of the image bearing means, by employing a unique configuration for the transfer means.
In an aspect of the present invention, transfer means is composed of a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with image bearing means via an image receiving member and directly over a predetermined effective contact width, and the effective contact width is set to be larger than the effective charging width of charging means and larger than the effective transfer width.
That is, according to an aspect of the present invention, there is provided, as an image forming machine which attains the above main object, an image forming machine comprising image bearing means moved sequentially through a charging zone, an exposure zone, a development zone, a transfer zone, and a cleaning zone, charging means for charging the image bearing means in the charging zone, exposure means for selectively static-eliminating the image bearing means in the exposure zone to form an electrostatic latent image on the image bearing means, reversal development means for developing the electrostatic latent image into a toner image in the development zone, transfer means for transferring the toner image on the image bearing means onto an image receiving member in the transfer zone, and cleaning means for removing a toner remaining on the image bearing means in the cleaning zone after transfer, the transfer means including a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, and wherein
the charging means charges the image bearing means over a predetermined effective charging width, the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with the image bearing means via the image receiving member and directly over a predetermined effective contact width, and the effective contact width is larger than the effective charging width and larger than the effective transfer width.
The effective contact width is preferably larger than the width of the image receiving member of a maximum size. In a preferred embodiment, the transfer means includes belt cleaning means for removing an adhered toner from the face side of the transfer belt, and the effective cleaning width of the belt cleaning means is larger than the effective contact width. The effective transfer width is preferably smaller than the effective charging width. The transfer voltage applicator means can be composed of a voltage applicator roller which is formed from an electrically conductive material and to which the transfer voltage is applied. There can be disposed pressure rollers which are arranged on both sides of the voltage applicator roller and which act on the back side of the transfer belt to press the face side of the transfer belt against the image bearing means. Advantageously, the pressure rollers are concentric with the voltage applicator roller. The voltage applicator roller and the pressure rollers are preferably fixed to an electrically conductive common support shaft which is rotatably mounted. Preferably, the transfer voltage is applied to the voltage applicator roller via the common support shaft, and the pressure rollers are formed from an insulating material.
In other aspect of the present invention, the transfer means is composed of a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with the image bearing means via an image receiving member and directly over a predetermined effective contact width, the effective contact width is set to be larger than the effective development width, the effective cleaning width and/or the effective charging width and larger than the effective transfer width, and spacing setting rollers or various sealing members are arranged in the effective contact width.
That is, according to the other aspect of the present invention, there is provided, as an image forming machine which attains the aforementioned object, an image forming machine comprising image bearing means moved sequentially through a charging zone, an exposure zone, a development zone, a transfer zone, and a cleaning zone, charging means for charging the image bearing means in the charging zone, exposure means for selectively static-eliminating the image bearing means in the exposure zone to form an electrostatic latent image on the image bearing means, reversal development means for developing the electrostatic latent image into a toner image in the development zone, transfer means for transferring the toner image on the image bearing means onto an image receiving member in the transfer zone, and cleaning means for removing a toner remaining on the image bearing means in the cleaning zone after transfer, the transfer means including a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, and wherein
the reversal development means develops the image bearing means over a predetermined effective development width, the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with the image bearing means via the image receiving member and directly over a predetermined effective contact width, and the effective contact width is larger than the effective development width and larger than the effective transfer width.
In a preferred embodiment, the development means includes a development housing having an opening at a site facing the image bearing means, developer applicator means disposed in the development housing and adapted to act on the image bearing means through the opening, an upstream sealing member disposed in the development housing and having a free end brought into contact with the image bearing means upstream from the developer applicator means, a pair of side sealing members disposed in the development housing and brought into contact with the image bearing means on both sides of the developer applicator means, and/or a pair of spacing setting rollers rotatably mounted on the development housing and brought into contact with the image bearing means on both sides of the developer applicator means; and the width of the upstream sealing member, the length between the outside ends of the pair of side sealing members, and/or the length between the outside ends of the pair of spacing setting rollers are or is larger than the effective development width and smaller than the effective contact width.
According to the other aspect of the present invention, there is also provided, as an image forming machine which attains the aforementioned object, an image forming machine comprising image bearing means moved sequentially through a charging zone, an exposure zone, a development zone, a transfer zone, and a cleaning zone, charging means for charging the image bearing means in the charging zone, exposure means for selectively static-eliminating the image bearing means in the exposure zone to form an electrostatic latent image on the image bearing means, reversal development means for developing the electrostatic latent image into a toner image in the development zone, transfer means for transferring the toner image on the image bearing means onto an image receiving member in the transfer zone, and cleaning means for removing a toner remaining on the image bearing means in the cleaning zone after transfer, the transfer means including a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, and wherein
the cleaning means removes the toner remaining on the image bearing means over a predetermined effective cleaning width, and the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with the image bearing means via the image receiving member and directly over a predetermined effective contact width, and the effective contact width is larger than the effective cleaning width and larger than the effective transfer width.
In a preferred embodiment, the cleaning means includes a cleaning housing having an opening at a site facing the image bearing means, a cleaning blade disposed in the cleaning housing and having a front edge portion pressed against the image bearing means, an upstream sealing member disposed in the cleaning housing and having a free end brought into contact with the image bearing means upstream from the cleaning blade, and/or a pair of side sealing members disposed in the cleaning housing and brought into contact with the image bearing means on both sides of the cleaning blade; and the width of the upstream sealing member, and/or the length between the outside ends of the pair of side sealing members are or is larger than the effective cleaning width and smaller than the effective contact width.
According to the other aspect of the present invention, moreover, there is provided, as an image forming machine which attains the aforementioned object, an image forming machine comprising image bearing means moved sequentially through a charging zone, an exposure zone, a development zone, a transfer zone, and a cleaning zone, charging means for charging the image bearing means in the charging zone, exposure means for selectively static-eliminating the image bearing means in the exposure zone to form an electrostatic latent image on the image bearing means, reversal development means for developing the electrostatic latent image into a toner image in the development zone, transfer means for transferring the toner image on the image bearing means onto an image receiving member in the transfer zone, and cleaning means for removing a toner remaining on the image bearing means in the cleaning zone after transfer, the transfer means including a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, and wherein
the charging means includes a corona discharger for charging the image bearing means over a predetermined effective charging width, and a pair of spacing setting rollers rotatably mounted on the corona discharger and brought into contact with the image bearing means on both sides of the effective charging width, and the length of the outside ends of the pair of spacing setting rollers is larger than the effective charging width and smaller than the effective contact width.